Tom Shafer

Low-e glass: the breakdown

September 18, 2014

Recently, window manufacturers have stopped offering clear glass. No, that doesn't mean you can only buy color-tinted windows now - but it does mean you can only get windows with low-e glass. And that's good news all around. Low-e glass gives you more energy-efficient windows, and in turn, a more energy-efficient home. The next time you update your windows, you'll be doing something good for the whole house! After installing replacement home windows with low-e glass, make sure the next appraisal of your home notes the more energy efficient glass.

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While that all may sound great to you, you might have one lingering question: what the heck is low-e glass? In industry terms, it, it lowers solar heat gain and reflects radiant energy to its source. In layman's terms, it keeps heat in during the winter and out during the summer by reflecting the heat back to where it came from - so either your home's heating system or the sun. Low-e glass's ability to reflect that radiant heat is measured with two factors:

  1. U-value. The u-value number tells you how fast glass allows heat to move from outside the home to inside the home. Its measurement is in hundredths of one and lower is better, so for example, u-value of .32 is better than u-value of .50.
  2. Solar Heat Gain Coefficient. This measures how fast the window allows solar energy from the outside to the inside. Again it is measured in hundredths and lower it better -- so .21 is better than .35.

Let's take a look now at just how much low-e glass can save you. Say we have a home in Jackson, Mississippi that has three types of windows. All three have vinyl frames, but one has clear, insulated glass, another has a low solar heat gain glass, and the third has a medium solar heat gain glass. The full results of this experiment can be explored at the The Efficient Windows Collaborative. In brief, a home that has all energy-efficient, low solar heat gain, low-e glass in the windows (LSG Low-E) will cost $506 to heat and cool while a home that has windows with only clear glass will cost $615. (Note: This example assumes a single story home with typical sun exposure and 15% window area.)

In addition to saving you money, having widows that meet Energy Star criteria has been shown to make the home more sellable, easier to finance, and eligible for utility company incentives. Overall, windows with low-e glass will pay for themselves many times over during the life of the home, making them worth every penny.


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